Bundle MinGW runtime DLLs into Windows wheels (delvewheel)

[stoiver]

Fixes #150.

Problem

cibuildwheel repairs Linux wheels (auditwheel → manylinux) and macOS wheels (delocate) by default, but does not run a repair step on Windows. The extension is built with MinGW, so the published win_amd64 wheels ship without their runtime DLLs and fail to import on a clean Windows Python:

ImportError: DLL load failed while importing _internals: The specified module could not be found.

_internals.*.pyd imports libgcc_s_seh-1.dll and libstdc++-6.dll (confirmed via pefile), neither of which is bundled in the wheel or present on a stock Windows Python. This also breaks downstreams — e.g. pip install anuga, which depends on meshpy.

Fix

Add the documented cibuildwheel Windows repair step using delvewheel, which bundles the dependent DLLs and rewrites the load paths so the wheel is self-contained:

CIBW_BEFORE_BUILD_WINDOWS: "pip install delvewheel"
CIBW_REPAIR_WHEEL_COMMAND_WINDOWS: "delvewheel repair -w {dest_dir} {wheel}"

The MinGW runtime DLLs are on PATH during the build (that's how meson finds gcc), so delvewheel locates and bundles them. Linux and macOS builds are unaffected.

Verifying

This PR's Build wheels run produces the Windows wheels; the repaired wheel should contain the bundled DLLs under meshpy.libs/ (e.g. delvewheel adds libstdc++-6, libgcc_s_seh-1, libwinpthread-1), and import meshpy.triangle then works in a clean venv with no MinGW on PATH.

🤖 Generated with Claude Code

[inducer]

Thanks for this PR. It turns out that cibuildwheel 4 has started automatically running delvewheel:

https://cibuildwheel.pypa.io/en/stable/changelog/#v400

The bump to that went in this morning in #152. Does that make this PR redundant? (You can grab built wheels from the wheel build artifacts I think, in case that's helpful.)

[stoiver]

Confirmed redundant — closing. I verified the Windows wheel built from main right after #152 (cibuildwheel 3.4.1 → 4.0.0) merged: cibuildwheel 4.0 auto-runs delvewheel, and the wheel now bundles the previously-missing MinGW runtimes in meshpy.libs/ (libstdc++-6, libgcc_s_seh-1, libwinpthread-1, hash-mangled, plus a DELVEWHEEL marker in dist-info). So cibuildwheel 4 does automatically what this PR did manually — no need for the explicit delvewheel step. Thanks for the pointer! (Note #150 isn't fully resolved for consumers until a new release carries these wheels to PyPI — the current 2025.1.1 wheels there predate the fix.)